The present invention relates to a method for searching a transmitter with a detector, which includes at least a first and a second antenna for receiving a transmit signal of the transmitter, wherein the transmit signal includes transmit pulses emitted with a certain transmit pulse period, as well as a position determining device for determining at least one orientation variation of the detector, comprising the following steps: a) detecting the vectorial magnetic field strengths of the field emitted by the transmitter in at least two dimensions for at least a first and a second measurement point relative to a reference axis of the detector carried by a searcher; and b) detecting at least one orientation difference between at least the first and the second measurement point. Moreover, it relates to a detector for searching a transmitter including at least a first and a second antenna for receiving a transmit signal of the transmitter, a position determining device for determining at least one orientation variation of the detector, and a processing device coupled at least to the first and the second antenna and the position determining device, wherein the processing device is configured to detect the vectorial magnetic field strengths of the field emitted by the transmitter in at least two dimensions for at least a first and a second measurement point relative to a reference axis of the detector carried by a searcher as well as an orientation difference of the detector between at least the first and the second measurement point.
In the following, the present invention is explained in more detail using the example of an avalanche victim detector. However, it is applicable to other types of detectors without restriction, for example in order to search for persons in a destroyed building.
The technology of today's avalanche victim detectors is based on tracking a magnetic field line. In this connection, FIG. 1 shows the position of a searcher 12 carrying an avalanche victim detector 18, as well as the position of a buried victim 14 carrying a transmitter 15 with a transmitting antenna 16. As it is clearly recognizable, the searcher 12, if he is not on the axis of the transmitting antenna 16 by chance, is thus always guided in a—sometimes wide—curve to the transmitter 15, that is to the buried victim 14. The magnetic field lines are the curves emanating from the transmitting antenna 16 illustrated in FIG. 1.
This approach has the following disadvantages:                The searcher has to travel a farther way than actually required.        Only the direction of the field line (field vector) is available along the curved guide path. Due to the curvature, the actual position of the transmitter cannot be simply inferred from it. Thus, the searcher cannot know where—related to his own position—the transmitter is actually located. A searching strategy is not possible in this sense.        The measurement of the direction and field strength is always local. Two measurements in different positions cannot be related to each other. Thus, improvement of the accuracy by inclusion of prior measurements is not possible.        The following measurement cannot be inferred from the direction and distance of prior measurements. In case of loss of the transmit signal, for example as a result of superposition in the multi-search, thus, the search cannot be simply continued based on a target already calculated before.        
In the range of the fine search, that is in the immediate environment of the buried victim, it is necessary to determine the perpendicular projection of the buried victim to the snow surface (projection point) on the one hand, also his burial depth on the other hand. Since the vertical orientation of the transmitting antenna is generally unknown, near the transmitter, usually in a distance of two to three meters, the direction indication is turned off. Then, the searcher changes his searching strategy. He does no longer follow the directional arrow, but rather maintains the current orientation of the detector. By slow movement back and forth on the one hand as well as left/right movement on the other hand, he searches the position with the least distance indication corresponding to the maximum field strength. For determining the depth, usually, a linear or square combination of the field strength measured in three axes is used today.
This approach is associated with several disadvantages:                The search for the maximum field strength requires high concentration and causes the highest time portion of the entire searching operation.        The linear or square combination of the field strengths only results in an approximate depth estimate.        The projection point can only be approximately correctly determined with existing methods with oblique transmitting antenna.        
Another known approach is in determining the position of the searcher in the geostationary coordinate system by means of GPS. Thereby, a known position in the geostationary coordinate system can be associated with each vectorial field measurement. If sufficient measured values are present, the location of the transmitter can also be calculated in the stationary coordinate system.
Therein, the drift of the GPS measurement caused by system is disadvantageous. During the period of a search, the measured location coordinate drifts by several meters. As a result, the location of the transmitter cannot be estimated with the accuracy required for the rescue of the buried victim.
DE 10 2008 016 137 A1 solves this problem by employing stationary reference stations in addition to the searching receiver variable in location, which also receive the GPS signal and are all subject to the same drift. Thereby, the movement of the searcher relative to the reference stations can be determined free of drift. In result, this method corresponds to the application of differential GPS.
However, in practice, carrying and applying the reference stations is a considerable disadvantage. Applying the reference stations in the searching field alone causes an expenditure of time, which cannot compensated for any more thereafter by an accelerated search.
A further possibility of establishing a relation between a geostationary coordinate system and the magnetic field is in measuring and evaluating lateral and rotating movements of the detector. Thereby, the relative positional variation with respect to the geostationary coordinate system between individual field measurements can be determined such that in the ideal case each position can be represented except for a global (identical for all positions) displacement and rotation in the geostationary coordinate system. As above explained, the position of the transmitter (with the same displacement and rotation) can correspondingly be calculated.
In this approach, it is disadvantageous that the calculation of a translational variation from acceleration data requires double integration. Even least errors in the initial conditions (initial speed) result in constantly increasing positional errors already after short time.
As a variant, the orientation (the angle) could be determined from the measurement of the earth's magnetic field. However, this does not solve the problem of instability of the translational estimation.